1. Technical Field
The present invention relates to a circuit arrangement For correcting a gradation of image data adapted, for example, For a facsimile machine.
2. Background Art
Recent facsimile machines are provided with a circuit arrangement for adjusting the white/black (or bright/dark) gradation of image data obtained by scan-reading a manuscript. Generally, this type of circuit arrangement can adjust the gradation of image data like human eyes.
Conventionally, the image data obtained by a scanner is processed into a pixel signal and this pixel signal is sent to a binary coding circuit. The gradation adjusting circuit adjusts the pixel signal level in a similar manner as human eyes do before the pixel signal is transferred to the binary coding circuit. "Similar manner as human eyes do" means that the darkness of a dark segment of the pixel signal is emphasized whereas the brightness of a bright segment of the pixel signal is not emphasized.
When the gradation adjusting circuit is incorporated in a facsimile machine, a particular ROM is required for each scanner of the facsimile machine since optimum data for the correcting of the image data gradation vary with the type of scanner.
Therefore, if a single gradation correcting circuit should cope with all kinds of facsimile machine, the ROM of the gradation correcting circuit must be able to store a large variety of correction data. Otherwise, a number of ROMs should be prepared, each ROM being adapted to be optimum for a particular type of scanner, and one of the ROMs is selected and put into the facsimile machine when an designer knows which type of scanner is incorporated in the facsimile machine. In this case, the structure of the image processing circuit should be changed in accordance with the type of the scanner and this raises manufacturing cost.